A viewer gains a strong sense of depth by fusing the images recorded by the two eyes, and exploiting the difference (i.e., disparity) between these two images. Each eye detects a different image of an object, because the two eyes are separated by a certain distance (i.e., interpupilar distance—IPD), and furthermore, each eye observes the object from a different viewing point. The brain provides a stereoscopic perception to the viewer, by processing the two images detected by the two eyes. The ability of the brain to provide this stereoscopic perception decreases as the ratio between the IPD and the distance between the viewer and the object decreases, such that beyond a certain distance (i.e., about 600 meters) the viewer is unable to perceive the depth in the object.
Since the eyes of the viewer are separated along a horizontal line, there is a disparity between the two images along this horizontal line. The brain provides a perception of depth of a certain point of the object, according to the disparity associated with this point. Optical devices for providing stereoscopic perception are known in the art. Such devices include two image detectors, a display, and a processor connected to the image detectors and to the display. Since the image detectors are separated by a certain amount, each detects a different image of an object, from a different viewing point. The processor polarizes the right image and the left image at different polarization states, and provides these two polarized images to the display, for the display to display these two images side by side.
If a viewer wears a stereoscopic pair of glasses having two polarizers of the appropriates polarization states, the right eye detects only the right image displayed by the display, and the left eye only the left one, and in this manner the viewer gains a stereoscopic perception. This optical device is employed in medical devices for performing minimally invasive surgery (MIS), such as an endoscope, to provide the viewer a stereoscopic perception of an image of the inner wall of an organ (e.g., colon). The processor determines the depth of every point of the current image of the organ, according to the disparity associated with that point, and in case of a tumor in the colon, determines the volume of the tumor according to the depth data.
Reference is now made to FIG. 1, which is a schematic illustration of an optical device for providing a stereoscopic perception of an image of an object, generally referenced 50, as known in the art. Optical device 50 includes two lenses 52 and 54, two charge-coupled devices (CCD) 56 and 58, a processor 60 and a display 62. Processor 60 is connected with CCD's 56 and 58 and with display 62. Lenses 52 and 54 are located in front of CCD's 56 and 58, respectively. An object 64 is located in front of lenses 52 and 54. Each of the CCD's 56 and 58 is located behind lenses 52 and 54, respectively, at a focal length f respective of lenses 52 and 54.
The distance between object 64 and each of the lenses 52 and 54, in a direction parallel to an optical axis (not shown) respective of each of lenses 52 and 54, is referenced Z (i.e., depth). CCD's 56 and 58 receive light beams 66 and 68, respectively, from a point 70 on object 64, through lenses 52 and 54, respectively. Light beams 66 and 68 strike CCD's 56 and 58, respectively, to form projections 72 and 74 of point 70, respectively.
Projection 74 of point 70 on CCD 58 is represented by a projection 76 of the same point 70, on CCD 56. The distance between projections 72 and 76 of point 70 on CCD 56, along an epipolar line (not shown) on CCD 56, is referenced δ (i.e., disparity). Processor 60 determines the values of δ respective of different points on object 64, by processing the two images (not shown) detected by CCD's 56 and 58. Processor 60 determines the depth Z of each of these points, according to the respective value of δ. Processor 60 produces a right image and a left image polarized at different polarization states, for display 62 to display the right polarized image and the left polarized image. A viewer who wears a stereoscopic pair of glasses having a pair of appropriate polarizers, gains a stereoscopic perception, when viewing the display. When the viewer selects a point on the image by clicking the point by a mouse, processor 60 determines the depth of that point according to the disparity associated with that point, and display 62 displays the value of that depth.
U.S. Pat. No. 6,411,327 B1 issued to Kweon et al., and entitled “Stereo Camera System for Obtaining a Stereo Image of an Object, and System and Method for Measuring Distance Between the Stereo Camera System and the Object Using the Stereo Image”, is directed to a system for producing a stereo image and determining a disparity between the stereo images. The system includes a camera and a biprism. The camera is in form of a CCD. The biprism is in shape of a delta having a first incline, a second incline and a flat edge. The biprism is placed between an object and the camera, such that the first incline and the second incline obliquely face a lens of the camera. Furthermore, an edge of the biprism at which the first incline and the second incline meet, passes through an optical axis of the lens.
A real point located in front of the flat edge corresponds to a first imaginary point. A first distance between the real point and the first imaginary point along a plane parallel with the flat edge, depends on a distance between the real point and a center of the biprism, and on a first displacement angle of the biprism. The real point also corresponds to a second imaginary point, where a second distance there between along the plane, depends on the distance between the real point and the center of the biprism, and on a second displacement angle of the biprism.
The real point corresponds to the first imaginary point and to the second imaginary point, and in a frame of picture obtained in a single exposure, two images (i.e., stereo images) of the object are produced. A third distance (i.e., disparity), between two homologous points in the stereo images corresponding to the real point, is proportional to a sum of the first distance and the second distance. An object distance between the system and the object can be calculated from the third distance.
U.S. Pat. No. 6,624,935 B2 issued to Weissman et al., and entitled “Single-axis Stereoscopic Video Imaging System with Centering Capability”, is directed to a system for producing a stereoscopic image of an object. The system includes an imaging device, a single-axis optical system and an electronic shutter. The electronic shutter is located between the single-axis optical system and the imaging device.
When controlled by an appropriate electronic signal, the electronic shutter alternately blocks light transmission through each side of an appropriate aperture of the single-axis optical system. A right-eye image is generated when a left side of the electronic shutter blocks light transmission, and a left-eye image is generated when a right side of the electronic shutter blocks light transmission.